Why does the same ladybird come red-with-spots or solid black?
Turn over enough leaves in a Japanese garden and you'll eventually find two ladybirds that look like they belong to different families: one orange-red with a scatter of black spots, one glossy solid black with two or four red dots. They are the same species. Japanese entomologists have been tracking exactly which colour form turns up where, and when, since the 1950s — and the pattern they found is a genuinely useful case for telling apart two ecogeographic colour rules that keep getting merged into one. Here is the real science of thermal melanism, Gloger's rule, and Japan's own nami-tentō. (We'll teach you the Japanese words as we go.)
One species, four official colour forms
Harmonia axyridis, known in Japan as nami-tentō and worldwide as the multicoloured Asian lady beetle, is famous among geneticists for a textbook case of colour polymorphism: a single wild population contains several genetically distinct elytra (wing-cover) patterns living side by side, not a gradual blend. Kyoto University zoologist Taku Komai formally classified the main forms in the 1950s: succinea (pale reddish-orange ground colour with black spots), and three melanic forms with a dark ground colour instead — conspicua (black with two red spots), spectabilis (black with four red spots), and axyridis (black with many small red spots). All four exist in the same wild Japanese populations at the same time, and which one you're holding is set by a small number of alleles at a single genetic locus, not by diet, age, or damage.
Meet nami-tentō, Japan's most common ladybird
てんとう虫 — tentōmushi (ladybird beetle)
The everyday Japanese word for any ladybird is tentōmushi, literally "sun-facing insect" — a nod to the old belief that the beetle always climbs toward the light before taking flight. Harmonia axyridis is the nami-tentō ("common ladybird"), found across nearly the whole Japanese archipelago in gardens, rice paddies, and forest edges, where both adults and larvae eat aphids by the hundred. It is native to East Asia, but is also one of the world's best-studied invasive insects, having been deliberately introduced to North America and Europe as a biological pest-control agent starting in the 1980s, then spreading on its own far beyond where it was released.
Komai's maps: the colour ratio shifts by place and by season
分布 — bunpu (distribution)
Starting with Komai, Chino and Hosino's papers in 1950 and continuing through Komai's 1956 monograph, Japanese researchers plotted the bunpu, or geographic distribution, of the four colour forms across the country, plus how the ratio of pale to melanic beetles moved through the year at single sites. Both kinds of variation turned out to be real: the proportion of melanic beetles differs from region to region, and at any one location the mix also drifts across generations within a year. That double pattern — geographic and seasonal — is exactly what you'd expect if the colour forms aren't neutral decoration but are doing different jobs under different conditions, and it's what later research went looking to explain mechanistically.
Why a dark ladybird warms up faster in weak sun
体温 — taion (body temperature) · 気温 kion (air temperature)
Ladybirds, like other insects, can't generate much metabolic heat of their own — their taion depends heavily on absorbing warmth from sunlight. A darker surface absorbs more solar radiation than a paler one, so a melanic beetle heats up faster and can become active earlier in the morning, on cooler days, or earlier in spring than a pale one sitting in the same patch of sun. This is the thermal melanism hypothesis: in cooler climates or cooler seasons, the faster-warming melanic form gets an activity-time advantage, while in consistently hot summer weather that advantage shrinks or disappears, because every beetle already reaches an active body temperature easily regardless of colour. Laboratory work rearing H. axyridis at different fixed temperatures backs this up directly: a 2025 study found that the occurrence and size of dark elytral markings in wild-type beetles decreased as rearing temperature rose from 17.5°C to 32.5°C, confirming the colour response is temperature-sensitive plasticity layered on top of the underlying genetic polymorphism, not just fixed inheritance.
Thermal melanism is not Gloger's rule — even though both are about climate and colour
進化 — shinka (evolution)
It's tempting to file "colour tracks climate" under one label, but two distinct ecogeographic rules are at work here and they can pull in opposite directions. Gloger's rule, named after 19th-century zoologist Constantin Gloger, describes animals (classically birds and mammals) tending to be more darkly pigmented in warm, humid environments — largely because melanin also resists bacterial degradation of feathers and fur, and blocks UV damage, both bigger problems in humid heat. The thermal melanism hypothesis instead predicts more melanism in cooler climates or cooler seasons, for the completely different reason of faster solar heat gain. A single species can in principle show either pattern, or a mix, depending on which pressure dominates for that animal in that habitat — which is exactly why careful separately-tested cases like H. axyridis's temperature-linked elytral shinka, evolution studied down to the level of one genetic locus, matter more than a single blanket "climate explains colour" claim. Recent 2024–2025 work on other insects, including jewel beetles and scarab beetles, likewise finds that the two mechanisms can act on the same trait in opposite or size-dependent ways within a single group.
Why does a lab ladybird experiment matter to the bigger picture?
Colour is cheap to score and colour genetics in H. axyridis is unusually well resolved, which is exactly why it keeps getting used to test bigger ideas about how climate shapes pigmentation across the animal kingdom. But the Japanese data also carries a caution: earlier surveys found the pale succinea form's frequency changing across Japan from northeast to southwest without a clean, simple correlation to temperature or any other single climate variable measured at the time — a reminder that real field patterns are usually noisier than a laboratory temperature-plasticity result, and that non-random mating between colour forms (documented in this species independently of any thermal effect) can also shift the mix season to season. A one-mechanism story is a good hypothesis to test, not a fact to assume.
Common questions
Q. Is a solid black ladybird a different species from a red spotted one?
A. Not necessarily. In Harmonia axyridis (Japan's nami-tentō), the pale reddish succinea form and the dark melanic forms (conspicua, spectabilis, axyridis) are all the same species, differing at a small number of alleles at one genetic locus, classified by Kyoto University's Taku Komai in the 1950s.
Q. Why would a beetle benefit from being black?
A. A darker body absorbs more solar radiation and heats up faster in weak sunlight, letting a melanic beetle become active earlier in the morning or in cooler weather than a paler one — this is the thermal melanism hypothesis. A 2025 rearing-temperature study found dark elytral markings in H. axyridis decreased as temperature rose from 17.5°C to 32.5°C, consistent with a temperature-linked response layered on the genetic polymorphism.
Q. Is thermal melanism the same thing as Gloger's rule?
A. No, though they're often confused. Gloger's rule predicts darker pigmentation in warm, humid climates, largely for melanin's anti-bacterial and UV-protective properties. The thermal melanism hypothesis predicts more melanism in cooler climates instead, for faster solar heat absorption. The two mechanisms can point in opposite directions in the same species.
Q. Does the colour ratio of Japan's ladybirds actually track climate cleanly?
A. Not simply. Classic Japanese surveys found the pale succinea form's frequency shifting geographically across the country without a clean single correlation to temperature, and non-random mating between colour forms independently affects the seasonal mix — a reminder that field patterns are messier than single-mechanism lab results.
Q. Is nami-tentō the same ladybird that has become invasive elsewhere in the world?
A. Yes. Harmonia axyridis is native to East Asia including Japan, but was deliberately introduced to North America and Europe from the 1980s onward for aphid biocontrol, and has since spread as one of the world's most-studied invasive insects.
Where to find Japan's wildlife in the wild: our region-by-region wildlife guide. Or explore all 47 prefectures by recorded species in Ikimono Quest, built from open biodiversity data.
Written by naturalists. The science here reflects the established genetics of Harmonia axyridis colour polymorphism (Komai's classic Japanese work), the thermal melanism hypothesis, and Gloger's rule as distinct, independently documented mechanisms, plus recent (2024–2025) rearing-temperature and macroecological studies. Where field-level climate correlations are noisier or less settled than laboratory results, that is stated rather than smoothed over. Nature is full of exceptions — that's what makes it worth studying.